This disclosure relates generally to supplying power to electronic devices. More particularly, but not by way of limitation, this disclosure relates to a portable power source for the efficient transfer of power to an electronic device.
Rechargeable Batteries may be found in a variety of portable electronic devices including laptop, notebook and tablet computer systems, personal digital assistants (PDAs), cell phones, digital media players, cameras, etc. Current battery technology provides only a moderate amount of energy storage. As a result, individuals that make heavy use of their portable devices can find the need to recharge them while away from home or office. For this, individuals may use an AC powered charger, a backup or replacement battery, or an external battery pack used to charge the electronic device's internal battery. The latter type of device is often referred to as a “power bank.”
Many prior art power banks supply power through a specific type of connector adhering to a standard. For example, many power banks use a Universal Serial Bus (USB) connector. As a consequence, they supply voltage at a level required by the USB standard, nominally 5.0 volts. Similarly, because electronic devices comport to the same standard, they must be able to accept an input voltage at 5.0 volts. Batteries used in modern electronic devices however often have a terminal voltage of between 3.0 volts (fully, or near fully discharged) and 4.2 volts (fully, or near fully charged). Because of these voltage imbalances, prior art power banks will always need to boost their internal battery's output voltage to the USB's standard 5.0 volts, and an electronic device will always need to buck the incoming voltage to meet that of their internal battery (plus, perhaps, a small delta voltage needed to drive charging operations). This situation is shown in FIG. 1 in which power bank 100 and electronic device 105 each include a battery (110 and 115 respectively), a voltage level converter (120 and 125 respectively), and a USB connector (130 and 135 respectively). As shown, power bank 100's internal battery voltage 140 is between, for example, 3.0 and 4.0 volts. Through level converter 120 boost operation 145 takes this to 5.0 volts, transfer voltage 150. Level converter 125 in electronic device 105 uses buck operation 155 to then reduce transfer voltage 150 to its internal battery level 160 and/or a level needed by device 105's internal electronics (between, for example, 3.0 and 4.0 volts).
It is known that the power conversion efficiency of a boost operation is approximately equal to the power conversion efficiency of a buck operation: 83%. While the precise value will of course differ based on, for example, the type of switching elements used, the difference in output versus input voltage and the circuit's mode of operation (e.g., continuous versus discontinuous conduction modes), whatever this value is, contemporary power banks suffer such a loss twice (one loss in power bank 100 and another loss in electronic device 105).